(a) Field of the Invention
The present invention relates to a liquid crystal display and a method of modifying of an image signal.
(b) Description of Related Art
Liquid crystal displays (LCDs) include a pair of panels provided with field generating electrodes and a liquid crystal (LC) layer having dielectric anisotropy that is disposed between the two panels. The field generating electrodes generally include a plurality of pixel electrodes arranged in a matrix and connected to switching elements such as thin film transistors (TFTs), and a common electrode covering the entire surface of a panel and supplied with a common voltage. The field generating electrodes generate an electric field in response to applied voltages and liquid crystals disposed therebetween form a so-called liquid crystal capacitor. The liquid crystal capacitor is a basic element of a pixel along with a switching element.
The LCD applies voltages to the field generating electrodes to generate an electric field in the liquid crystal layer, and the strength of the electric field can be controlled by adjusting the voltage across the liquid crystal capacitor. Since the electric field determines the orientations of liquid crystal molecules and the molecular orientations determine the transmittance of light through the liquid crystal layer, light transmittance is adjusted by controlling the applied voltages to obtain desired images.
In order to prevent image deterioration due to long-time application of the unidirectional electric field, etc., polarity of the data voltages with respect to the common voltage is reversed every frame, every row, or every pixel.
As the LCD is increasingly used for displaying moving images, its slow response time has been receiving attention as a characteristic that needs improvement. The improvement in response time becomes even more desirable as the size and resolution of the display devices increase, creating even more of a delay in response time.
To compensate for the slow response speed, a method of applying a data voltage that is larger or smaller than a data voltage of an input image signal (i.e., an overshoot voltage or an undershoot voltage) to the pixel electrode has been suggested.
However, to apply the overshoot voltage when the LCD is in a normally black mode, and when the overshoot voltage corresponds to the maximum gray voltage, the data voltage corresponding to a white gray should be lower than the maximum gray voltage. Therefore, luminance of the LCD decreases.